Pulse train capture

[Ioannis]

I am trying to capture in an array the pulse width of a pulse train coming out of an HCS-301 chip.

The pulses are not always the same in a raw but the width should be fairly consistent as the Logic analyzer confirms, about 800μsec and 400μsec.

The PIC is the F886 at 8MHz so the resolution of PulsIn is 5μsec. Based on this the attached Excel shows some readings and though some pulses are in the correct range others are even 0 despite the use of PulsIn with a positive pulse trigger.

Cannot understand why this happens.

The complete pulse train consist of a guard width of 16ms, then 12 pulses of 50% 400/400μsec, a second guard width of about 4ms and then 66 pulses of 800 or 400μsec.

the code is this:

#config
Line1 = _DEBUG_OFF & _LVP_OFF & _FCMEN_OFF & _IESO_OFF & _BOR_ON
Line2 = _CP_OFF & _MCLRE_ON & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT
    __CONFIG _CONFIG1, Line1 & Line2
    __CONFIG _CONFIG2, _WRT_HALF & _BOR40V
#endconfig

OSCCON = %01110001 '8MHz Clock

'OSCCON = %01100001  '4MHz Clock

DEFINE OSC 8

;----- Configuration bits ------------------------------------------------



PORTA=0:PORTB=4:PORTC=0:PORTE=0

TRISA=%00000000 					'RA0: RED LED
									'RA1: Relay 1
									'RA2: Relay 2
                    				'RA3: Relay 3
                    				'RA4: Relay 4
									'RA5: 
									'RA6: 
									'RA7: 

TRISB=%00111111						'RB0: RF in
                                    'RB1: Channel 4 Latch button
                                    'RB2: Channel 3 Latch button
                                    'RB3: Channel 2 Latch button
                    				'RB4: Channel 1 Latch button
                                    'RB5: Autolearn Button
                    				'RB6: NC
                                    'RB7: NC
                    
TRISC=%00000100						'RC0:
									'RC1:  
									'RC2: 
									'RC3:
									'RC4:
									'RC5: 
									'RC6: TX
									'RC7: RX
									
TRISE=%00000001						'RE0: assigned to /MCLR
									
OPTION_REG.0=1						'PSA0 PRESCALER SELECT 1:1 TO 1:256
OPTION_REG.1=0						'PSA1
OPTION_REG.2=1						'PSA2
OPTION_REG.3=0						'PRESCALER TO: 1->WDT, 0->TMR0
OPTION_REG.4=0						'T0SE SOURCE EDGE 1->H TO L, 0->L TO H
OPTION_REG.5=0						'T0CS 1->FROM RA4, 0->FROM INT. CLOCK
OPTION_REG.6=0						'INT EDGE SELECT 0->H TO L, 1->L TO H
OPTION_REG.7=0						'PULL UP 1->DISABLE, 0->ENABLE

WPUB = %00111111

DEFINE HSER_RCSTA 90h
DEFINE HSER_TXSTA 20h
DEFINE HSER_BAUD 9600
DEFINE HSER_SPBRG 12  ' 9600 Baud @ 8MHz, 0,16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

'************************* ADC Setup
ADCON0 = 0
ADCON1 = 0	'Set PORTA/E digital
ANSEL  = 0  'all as digital inputs
ANSELH = 0  'all as digital inputs

BAUDCTL = %00010000         'Transmit inverted data (No MAX232 needed)

code        VAR byte[9] BANK0   ' Code
code1       var byte[66]
temp        var word
index       var byte

clear

hserout ["Waiting pulse",13,10]

while 1
    pulsin portb.0,0,temp
    if temp>3000 then
        if temp<4000 then     'find lomg header of 16ms
            for index=0 to 10
                pulsin portb.0,1,temp  'then skip 12 pulses of 50% Duty, 400ìsec
            next index
            for index=0 to 65   'now collect 66 pulses of aroun 800 or 400 ìsec
                pulsin portb.0,1,temp
                code[index]=temp
            next index
            for index=0 to 65
                hserout [#code[index],13,10]  'display pulse train
            next index
            hserout ["End",13,10]
        endif
    endif
wend

Ioannis